1. Field of the Invention
The present invention relates to a surface position detection apparatus and, more particularly, to a focal point position detection apparatus suitable for, e.g., a semiconductor manufacturing apparatus.
2. Related Background Art
As a conventional focal point position detection apparatus in a semiconductor detection apparatus, as disclosed in Japanese Laid-Open Patent Application No. 56-42205 proposed by the assignee of the present application, an oblique incidence type focal point position detection apparatus is used. This apparatus obliquely projects detection light onto a semiconductor wafer arranged at a position where a mask pattern is transferred by a projection lens.
The focal point position detection apparatus uses the surface of a semiconductor wafer as a surface to be detected (to be referred to as a detection surface hereinafter), and projects a slit-like pattern onto the detection surface in a direction wherein the longitudinal direction of a slit becomes perpendicular to a plane defined between incident light and reflected light, i.e., a plane of incidence. The apparatus re-focuses the reflected light on a detection means comprising a photoelectric transducer, thereby detecting an incident position of the reflected light on the detection means.
When the surface as the detection surface of the semiconductor wafer is displaced in the vertical direction (i.e., it approaches or is separated along the optical axis direction of the projection lens), slit reflected light incident on the detection means is image-shifted in a direction parallel to the plane of incidence, i.e., in the widthwise direction of the slit in correspondence with the vertical displacement. By utilizing this effect, the apparatus detects an image shift amount, thereby detecting the vertical position of the surface of the semiconductor wafer. In this manner, it is discriminated whether or not the wafer surface coincides with a focusing reference position of the projection lens, i.e., a conjugate plane with a lens projected by the projection lens.
In this case, the apparatus re-focuses light reflected by a small slit-like pattern region projected on the detection surface, and detects an average position on the small slit-like detection region.
In recent years, along with the increase in degree of integration of LSIs (Large Scale Integrations), demand has arisen for transferring a micropattern onto an exposure region (shot region) on a wafer. In order to meet this demand, a numerical aperture NA of the projection lens is increased. Thus, since the focal depth of a projection objective lens becomes shallow, it is important to accurately and reliably align the exposure region at the focal point position (within the focal depth) of the projection objective lens.
The area of the exposure region by a projection/exposure apparatus is also increasing. Thus, an LSI chip having an increased exposure area is exposed in a single exposure operation, or a plurality of LSI chips are exposed in a single exposure operation. For this reason, it is important to accurately and reliably align the overall exposure region with an increased area with the focal point position (within the focal depth) of the projection objective lens.
Furthermore, when a plurality of LSI chips are exposed at the same time, and when the size of an LSI chip to be exposed (the size of the exposure region) is to be changed, illumination light for position detection cannot be radiated on a proper position on the detection surface, and the position of the projection light must be changed.
In order to solve this problem by the conventional focal point position detection apparatus in this situation, position detection on the exposure region on the wafer must be performed at a plurality of positions.
For this reason, a stage, which places a wafer thereon, may be properly moved so as to project slit light from the focal point position detection apparatus onto necessary detection positions and to detect these positions. However, in this case, a decrease in throughput is inevitable.